javaType errorMedium

ArrayStoreException with covariant array assignment

Time: 0:00

BugFind the bug and fix the code

What it should do

Store string in array and return string. Example: storeObjectInArray("test") -> "test"

What happens instead

java.lang.ArrayStoreException thrown when storing wrong type into covariant array

public class Main {
    public static String storeObjectInArray(String val) {
        // Array covariance allows assigning Integer[] to Object[], but runtime checks throw
        Object[] arr = new Integer[1];
        arr[0] = val; // Throws ArrayStoreException at runtime!
        return (String) arr[0];
    }

    public static void main(String[] args) {
        System.out.println(storeObjectInArray("test"));
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

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public class Main { public static String storeObjectInArray(String val) { // Array covariance allows assigning Integer[] to Object[], but runtime checks throw Object[] arr = new Integer[1]; arr[0] = val; // Throws ArrayStoreException at runtime! return (String) arr[0]; } public static void main(String[] args) { System.out.println(storeObjectInArray("test")); } }

ArrayStoreException with covariant array assignment

What it should do

What happens instead

More type errors to practise

ArrayStoreException with covariant array assignment

What it should do

What happens instead

More type errors to practise